HP XP Business Copy Software - Manual (Page 15)

The operation for splitting all the pairs in the same CTG is similar to the operation for splitting
pairs when a copy group is specified by using XP for Business Continuity Manager Software™.
However, the operation for splitting pairs in a CTG works in Quick Split, so you cannot specify
Steady Split. You cannot specify the split time when using the PPRC command to split pairs.
The split time indicates when you want to store the S-VOL data to the T-VOL.
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Triggers for the change of pair status to Split
The performance in the V-Split or SP-Pend state is different depending on the value of system
option mode 459 (ON or OFF, OFF by default) and whether the T-VOL or the volume in a
pool that is associated with the T-VOL is an external volume or an internal volume.
Table 1 Performance in the V-Split or SP-Pend state is different depending compared to option
mode 459 and the type of T-VOL.
PSUS(SP) or COPY(SP) S-VOL System option mode 459
The pair status changes to Split after
all the differential data are copied to
the cache in the storage system. Internal volume OFF
External volume
The pair status changes to Split after
all the differential data are copied to
the cache in the storage system and
the destage in the external storage
system. Internal volume ON
External volume
Suspend Pair Operation
The ShadowImage for Mainframe suspend pair operation suspends the update copy operations
to the T-VOL of the pair. When an SIz pair is suspended, the XP storage system stops performing
update copy operations to the T-VOL, and the pair status changes to suspended. The storage system
continues accepting write I/O operations to the S-VOL, and marks the entire S-VOL track as
difference data. When a pairresync operation is performed on a suspended pair, the pair status
changes to resync and the entire S-VOL is copied to the T-VOL. While the pairresync operation for
a split pair can be very fast, the pairresync operation for a suspended pair will take as long as
the initial copy operation.
The XP storage system will automatically suspend an SIz pair when it cannot keep the pair mirrored
for any reason. When the storage system suspends a pair, sense information is generated to notify
the host. The storage system will automatically suspend an SIz pair under the following conditions:
•
When the storage system detects an error condition related to an update copy operation, and
•
When the differential bitmap in shared memory is lost (for example, due to offline microcode
exchange). This applies to SP-pend and V-split pairs only. For duplex, split, resync, or resync-r
pairs, the pair is not suspended but the entire S-VOL (T-VOL for reverse copy) is marked as
difference data.
Resynchronize Pair Operations
To change the status of the pairs from Split to Duplex, or from Suspend to Duplex, you must
resynchronize the pairs. ShadowImage for Mainframe allows you to perform two different types
of pairresync operations: forward pairresync operation (Normal Copy and Quick Resync) and
backward pairresync operation (Reverse Copy and Quick Copy). Forward pairresync means
copying S-VOL data to the T-VOL, and backward pairresync means copying T-VOL data to the
S-VOL.
•
Normal Copy (forward pairresync in normal speed)
The normal resync operation first edits the differential bitmap of S-VOL and T-VOL, and then
(see
Figure 6 (page 17) ) resynchronizes the T-VOL with the S-VOL based on the information
ShadowImage for Mainframe Operations 15